1. Field of the Invention
This invention relates to a transaction system, and in particular it relates to a system including a terminal for reading from and writing to an electronic token which has an onboard data processing capability. Such a token is often in the form of an elongate card and may be termed a "Smart Card". The terminal may be a stand alone unit with which data held within the token can be read or altered or alternatively the terminal may be connected by a remote or local link to an external host such as a bank's computer.
2. Background Information
Systems of this type have become well established in recent years and generally take the form of a terminal fixed at a certain place, such as a bank, and a token which is portable and is issued to an individual who carries the token around and brings it to the terminal when a transaction is deemed necessary. The system may be of the contact type in which the token must physically touch the terminal in order for communication to be established or may be of the contactless type which utilises for example, inductive coupling. This invention is related to the latter-mentioned type of coupling.
It is evident that in this type of system, a terminal is in communication with a token only for short periods of time but it is important that, when a token is brought towards the terminal, the terminal recognises this and is able relatively quickly to establish communication. It is preferable that the user does not have to `switch on` the terminal each time he wants to use it. Thus, in inductively coupled systems which use a carrier wave transmitted from the terminal to the token the terminal may be permanently energised so that when the token is brought towards the terminal it is immediately powered up. In an alternative form as described in GB 2208025 A, the terminal is arranged to transmit the carrier signal at a relatively low stand-by level and, after detecting a token, to raise the level of the carrier to a higher level equal to the operating level. Since the carrier signal is permanently on, albeit at a low level, the terminal still consumes a considerable amount of power when in its `dormant` mode.
The present invention arose from a need to reduce still further this power requirement.